Shutters which fold over window and door openings have been in use for a long time. The louvers of the shutter are either fixed or pivoting. Pivoting louvers are typically hinged at their end points by a pair of projections which mate with a pair of bearing bores. If the cut of the louvers at their ends adjacent the hinged support is closely dimensioned to the typically flat members containing the bearing bore, the light passing through the gap of closed shutters should be sufficiently attenuated.
As the light between adjacent pairs of louvers, typically vertically upward or downward of a given louver, this continues to present a problem. Most louvers have main edges along the major part of their length which is rounded. In order for the louvers to act in concert, each louver typically carries a "U" shaped staple attached near the center of its length, and typically on the side with the "fattest" or thickest and most gently curving portion. Put another way, where the louvers are shaped more like an airplane wing, the front edge which is thicker and has a more rounded surface is selected to accept attachment with a staple. Since the thickness of the louvers, even at the thickest edge are still limited, the "U" shaped staples have each leg located longitudinally along the centerline of the thickest edge. A line through the points on the edge of the louver where a staple enters is longitudinal to the louver.
In order for the louvers to act in concert, an simultaneous actuation handle is used having a series of "U" shaped staples which are arranged so that the "U" shaped staples have each leg located longitudinally along the centerline of the simultaneous actuation handle. The curve of each of the "U" shaped staples of the simultaneous actuation handle engage the curve of each of the "U" shaped staples of the louvers. The simultaneous actuation handle may be adjusted to adjust the angles of all of the louvers simultaneously. A groove is typically made into the frame adjacent one of the last louvers of the series in order to accommodate a tip end of the simultaneous actuation handle when the louvers are adjusted to their most closed position, when the simultaneous actuation handle is brought most closely against the louvers and frame.
In this system, there is a significant amount of "play" or looseness between the louvers and the adjustment handle. This looseness can cause some of the louvers not to close in complete concert with the others. Compounding this problem is the position of the louvers at full close. In most louver systems, the full close position is one at which the louvers tangentially overlap each other. The "fat" front of the airfoil louver shape is angled to a position where the rounded front only tangentially contacts the relatively sharper trailing edge of the adjacent louver. Assuming the light leakage at the ends of the louvers abutting contact with the end strips is adequately controlled, the limitation of a tangential contact elsewhere in the louver set represents a huge source of mis-alignment and leaking light. Where the louvers warp, or where either the trailing or leading edge is not cut 100% linearly, or where the pivot bore is ever so slightly mis-aligned, the louvers will not achieve significant light blockage in the closed position.
In addition to these problems, the problem of connection to the "U" shaped staple to the louvers is one which is not only productive of error in light blockage, it is also ultimately destructive to the louver, especially where the louvers are relatively small and the staples are of significant size. Where the "U" shaped staples enter even the "fat" or leading edge portion of the louver, there may be precious little additional material within the louver to accommodate the lateral forces of the staple. Where the louvers are wood, they will splinter and crack and may chip large amounts of material away. Where this occurs at the last step of manufacture there is a tremendous waste since the remaining parts of the shutter which are in good repair are typically discarded. The use of smaller staples is not always the answer, since in high speed manufacture the staples may bend.
The use of the staples in high speed manufacture also carries the problem of differences in the density of material being used for the shutters. Where wood is used, the staples used for the louvers might be entering a volume of wood which is of significantly higher or lower density than the average. The staple might go in too far to create both an increased splintering problem, as well as an alignment problem with respect to the adjustment handle. For staples in the adjustment handle, this may also be a problem.
The problems enumerated above require a high degree of precise manufacturing, inspection and tollerancing in order to yield a shutter set which can block out the last degree of light. As such, the cost of production rises and high quality high blockage shutters are then placed out of economic reach for ordinary purchasers of such shutters. In addition, where materials change over time, either through moisture exposure, heat cycling and stress, a system which relies upon the integrity of a tangential line between two edges to shut out light the shutters produced will experience a diminution of quality over time.
Another problem relates to the angular pivoting displacement of each louver with respect to the staple in the tangential end of the larger end. In order to try to achieve a nearly 160.degree. rotation of the louvers in order to achieve a range of motion from closed, or as nearly closed as possible, to allowing upwardly directed light, to horizontally directed light, to allowing downwardly directed light, the staples are not in alignment with the mid-plane of the louver. The staples are located to one side of the midplane to insure that in the closed position that the staple is still directed away from the mid-line enough that the simultaneous actuation handle can still function. This off-center mounting which facilitates closure in one direction militates against closure of the louvers in the other direction. Moreover, this mounting insures that the sealing of light between louvers will be along edges which are not the end edges, and edges for which warping of the louvers will admit light.
What is needed is a system which will enable louvers to seal out light by contact on other than their normal tangential contact to one side of the other of the end surfaces. Elimination of the "U" shaped staples inserted directly into the leading edge of the louvers is also needed to reduce scrap and damage, and to eliminate a common failure mode which may be essentially un-repairable in shutters which have been in service for some time.